I tested Obi2 on some posts of blogs that I follow. It says 6-7-8. Then I tested my own blog post, obi2 says its level is 7 :))
T13 Grade = 10 (1st year in high school)
You can make it as complicated as you like. If you want to make it simple (as I do), you plot average words per sentence on one axis, and average characters per word on the other. For a given language, texts at any given LingQ level will fall on a banana-shaped curve. Higher LingQ levels have banana-shaped curves to the top and the right of the graph, lower LingQ levels fall to the bottom and the left.
Because different languages have different structure (eg use of particles vs use of prefixes), the curves of different languages will be at different places on the graph.
Note this analysis isn’t going to tell you whether you will UNDERSTAND a given piece of text (or the accompanying audio file). Just what LingQ level it should be placed in based on its readability.